The present invention relates generally to liquid dispensing devices and methods, and more particularly to such devices and methods wherein a mechanical flow meter is used to measure the volume of liquid dispensed.
More particularly, the present invention relates to a liquid dispenser incorporating a mechanical flow meter having a rotating mechanical output responsive to the passage of liquid through the meter. In such a meter, each mechanical rotation of a rotary output shaft ordinarily corresponds to a specific volume of dispensed liquid. The meter output is typically connected to a pulser which generates a fixed number of pulses per revolution of the output shaft. The pulses are then processed by conventional electronic data display means for indicating data such as quantity of liquid dispensed, price per unit, and total price of the sale.
A problem arises in the aforementioned dispenser in that the volume of liquid through a mechanical flow meter corresponding to a given rotational output of the meter varies to some extent due to variations in dimensional parameters, as well as mechanical wear and leakage of meter components. As a result, the volume of liquid dispensed as reflected by the data display means does not always correspond to the actual volume of liquid flowing through the meter. Accordingly, it is necessary to calibrate the flow meter from time to time to insure that the dispensed liquid volume reflected by the data display means corresponds as nearly as possible to the volume of liquid dispensed through the flow meter.
In the past, meters in liquid dispensing devices have been provided with means to change the displacement thereof so that the volume of liquid dispensed per rotation of the meter shaft corresponds in fixed relation to the number of delivery pulses produced and, therefore, the volume displayed by the data display means. This procedure involving mechanical calibration of the meter to alter the meter output entails not only the expense of a variable displacement meter, but also requires an attendant to manually perform multiple dispensing operations and make adjustments to the meter to arrive at the proper setting.
Another method of calibrating a meter, used particularly in pipeline applications, involves the use of large calibration barrels and barrel meter provers. The barrels are either permanently connected directly to the pipeline by means of elaborate valving, or are carried on a vehicle and temporarily attached inline of the flow of the pipeline, in order to monitor the output of the flow meter over dispensation of a fixed volume of liquid. A meter factor is then manually calculated and manually applied to all indicated readings from the meter.
An electronic register/calibrator apparatus is commercially available for use in a bulk flow application and includes a meter and a pulser, wherein a calibration factor is manually entered on thumbwheel switches for use to modify the pulser output prior to its use by the electronic register to reflect the accumulated volume of liquid flowing through the meter. Similar to the previously described procedure of mechanically calibrating the meter in a liquid dispensing device, calculation of the manually entered correction factor for use by the electronic register also requires an attendant to perform calibrated flow measurements and manually calculate the appropriate correction factor to be entered.
The described known methods of calibrating a mechanical flow meter to correct for variations in the volume of liquid passing through the meter per given meter output, all exhibit a common disadvantage of requiring human input or supervision. For instance, for a liquid dispensing device an attendant must manually perform dispensing operations and mechanically calibrate the meter by changing its displacement. In bulk flow metering, an operator must calculate a meter correction factor for entry into the electronic register apparatus or for application to volume readings taken therefrom. Because state and federal weights and measures agencies require performance of calibration tests at regular intervals, a substantial investment of time and expense is involved in maintaining a corps of trained personnel to travel to metering and liquid dispenser installations to perform such tests.
Another disadvantage of known meter calibration methods is that each time a meter is replaced or repaired, the time and expense of conducting a conventional meter calibration test is incurred.
A further disadvantage exists in that because current methods of meter calibration are so expensive and cumbersome, tests are not performed as frequently as is desirable.
A still further disadvantage of meter calibration methods involving the calculation of meter correction factors is that, as new factors are calculated, a records problem is created in maintaining the most current data.
Yet another disadvantage of known dispenser meter calibration methods is the need for calibration equipment external to the dispenser housing.
Several disadvantages are associated specifically with the use of large calibration barrels. For example, the barrels must be transported between installations, typically in the cargo compartment of a truck. Additionally, the barrel meter provers must be connected in some way to the liquid flow metering installation. Furthermore, manually actuable valving is typically employed in the aforementioned calibration barrels to provide bidirectional flow capabilities.